The need for control of the direction in which a bore hole progresses has always been desirable and the ability to reliably and accurately do so has improved markedly in recent years. With the advent of measurement while drilling, or MWD, directional drilling control became more frequently a drilling requirement.
Passive directional controls, applied historically, include the use and placement of stabilizers along the lower sections of the drill collars. Success of this system depended largely upon the drillers skill and experience. That approach is often considered more art than science.
Active directional controls, more recently employed, apply positive influence upon the drilling assembly and include the rather cumbersome use of whipstocks. More complex and about as capable are the systems for bending the active drill string just above the drill head. Hinge type devices are effective but tend to weaken the drill string. Permanently bent elements of the drill string usually require the use of drilling motors. Drilling motors, generally, do not have the ability to fully utilize the available hydraulic horsepower of the mud stream but, overall, their use is often economically advantageous.
When permanently bent sections of drill string are used, drilling motors are normally involved and straight hole drilling is usually accomplished by rotating the drill string. That rather deranges the force vectors in the lower end of the drill string and the drill head. In some formations, rotating a bent string produces unacceptable stresses in the lower drill string assembly.
It is desirable to provide means to deflect the course of the progressing drill head, only when needed for directional control, by directing a lateral force between the drill string and the well bore wall in the vicinity of the drill head. The reaction force at the drill head tends to deflect the course of the advancing bore hole. The drill string remains generally straight to better accept bit load vectors directed along the general centerline of the drill string. Rotary drilling without down hole motors can proceed if the side loading contrivance can remain rotationally stationary relative to earth while the drill string rotates.
It is therefore an object of this invention to provide means to extend an element from the drill string to engage, and apply a deflecting lateral force against, the well bore wall, and to retract the element when the lateral deflection is no longer needed.
It is still another object of this invention to provide apparatus that can be actuated to change between directional and straight hole drilling configuration by manipulation of the drilling fluid flow rate controls at the surface.
It is yet another object of this invention to provide apparatus to apply a deflection producing lateral force between a well bore wall and a drill string and maintain the lateral force producing means stationary while the drill string rotates to drill.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.